The Windows update hand-off shim was hardcoded to Microsoft Edge
(Find-EdgeExe), so machines whose default browser is Chrome still got
an Edge --app progress window, and every run leaked a throwaway
browser profile (hermes-update-ui-<pid>) under %TEMP% that was never
removed.
- Get-DefaultBrowserExe replaces Find-EdgeExe: resolves the OS default
browser from the UserChoice ProgId (https first, http fallback).
ChromeHTML -> Chrome, MSEdgeHTM -> Edge; any other ProgId returns
$null and degrades to the existing WinForms card.
- The dedicated --user-data-dir profile is now removed when the shim
closes, and stale hermes-update-ui-* leftovers from interrupted
runs are swept from %TEMP% in the same pass.
- --app + --user-data-dir is Chromium-only, so the whitelist is
intentionally limited to chrome/msedge; Edge keeps
--disable-features=msImplicitSignin to suppress the implicit MSA
sign-in that leaks into shim windows (#88410).
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